Vibrato apparatus



' Dec. 25, 1962 A. D. ARSEM E'rAL v 3,069,958

VIBRATO' APPARATUS Hummm Dec. 25, 1962 A D. ARsEM ETAL 3,069,958

VIBRATO APPARATUSv Filed Sept. 24, 1959V 2 Sheets-Sheet 2 United States Patent Office 3,069,958 Patented Dec. 25, 1962 3,069,958 VIBRAT() APPARATUS Alvan Donald Arsem, Buffalo, Fred H. Osborne, Snyder,

Ira M. Laurien, Williamsville, North Tonawanda, N.Y., assignors to The Wurlitzer Company, Chicago, Ill., a corporation of Ohio Filed Sept. 24, 1959, Ser. No. 842,126 .19 Claims. (Cl. 841.25)

This invention is concerned with the transducing of electrical oscillations into audible sound, and more particularly with the production of tremulant and vibrato effects in musical tones.

It has been `found hereto-fore that in the bass tones, say below 500 c.p.s., that a tremulant produced by simple arnplitude variation is satisfactory. However, such an effect is not satisfactory in the treble tones. A true vibrato is necessary in the treble tone, and this requires a frequency shift at a low frequency or vibrato cyclic rate. For best results, the frequency deviation produced by the vibrato mechanism should not be constant over the entire gamut of tones of the instrument. For the vibrato to be satisfactory, the frequency deviation has to be proportional to the frequency of each tone. This could be done -by frequency shifting the tone generator oscillators at the low frequency vibrato rate. In a properly designed oscillator, such a frequency deviation control will produce a frequency deviation proportional to the center frequency of the oscillator; however, for high deviations the stability -of the oscillator must be sacrificed. This results in an instrument which is difiicult to maintain properly tuned.

We have observed that the Doppler effect resulting from relative motion between a sound source and an observer produces a frequency shift which is proportional to the frequency of the note sounding. The percentage of frequency deviation has been observed to be dependent upon the velocity component toward or away from the observer. If the source moves toward the observer, the frequency is raised. Conversely, if the source moves away from the observer, the frequency is lowered.

Accordingly, it is an object of lthis invention to provide a superior vibrato for use with an electronic musical instrument, and more particularly to provide a vibrato relying on the Doppler effect.

It is another object of this invention to provide vibrato apparatus for use with electrical musical instruments having an improved moving sound source.

"In particular, it is an object of this invention to provide a superior vibrato apparatus for electronic musical instruments involving a rotating speaker movable toward and away from an observer.

Other and further objects and advantages of the present invention will be aparent from the following description when taken in connection with the accompanying drawings wherein:

FIG. l is a schematic diagram of a vibrato and tremulant arrangement in accordance with the present invention as incorporated in an electronic organ;

FlG. 2 is a schematic diagram of a similar, but more Complex arrangement utilizing a separate tone cabinet;

FIG. 3 is a perspective View of a tone cabinet used in conjunction with the schematic diagram of FIG. 2;

FIG. 4 is a side view of a vibrato and tremulant producing device constructed in accordance with the present invention;

FIG. 5 is a vertical sectional view therethrough as taken along the line 5-5 in FIG. 6;

FIG. 6 is a vertical sectional view taken substantially along the line 6-6 in FIG. 4;

FIG. 7 is a View similar to FIG. 5 showing a modification of the invention;

and Christian L. Flateau,

FIG. 8 is a detail view as taken substantially along the line 8 8 in FIG. 6; and

FIG. 9 is a fragmentary view of a modified loud speaker.

Before referring to the incorporation of the tremulant and vibrato device of the present invention in electronic musical instruments, as in FIGS. 1-3, it is thought that clarity best can be served by turning to FIGS. 4-6. A tremulant and vibrato device is identified in these figures generally lby the numeral 10, and includes a frame 12 conveniently including a pair of square side plates 14 of any suitable material, these plates being illustrated as metal. The plates are spaced apart `a few inches, and are held in such spaced relation 'by posts 16 at the four Icorners thereof secured by suitable screws 18 passing through the plates 14 and tapped into the posts. The bottom screws 18 also conveniently mount upright legs or posts 20 which are suitably secured to `a bottom plate 22. Acoustic insulation 24 preferably is afiixed to the top of the bottom plate 22. Suitable `bearings 26 are fixed on the inner faces of the side plates 14 and rotatably carry a tubular shaft 28.

A loud speaker frame 30 is mounted on the shaft 28 for rotation therewith, and includes a pair of diametral arms 32 in Iaxially spaced relation, a spacer sleeve 34 being interposed between these arms and encircling the tubular shaft 28. At one end of the arms, there is provided a bracket 36, conveniently of sheet steel, and having a pair of flanges 38 parallel to one another and to the arms 32. These brackets -are provided with circular apertures 4t) Ybehind 'which are mounted small loud speakers 42. The loud speakers are oriented away from one Ianother tangentially of the direction o-f movement thereof -as determined by rotation of the :bracket 30. In this embodiment of the invention, the loud speakers 42 `are illustrated as being round or circular lo-ud speakers having 4approximately four inch cones.

` The speaker bracket or frame 30 at the ends o-f the arms 32 opposite the speakers 42 is provided with a cross member 44 having a radially disposed stud 46 threaded therethrough. A lock nut `48 preferably is provided to secure the stud in adjusted position, and a weight 50 is threaded on the stud, a jam nut 52 preferably -being associated therewith for counterbalancing the speakers and lbracket.

The tubular shaft 28 extends beyond the back plate 14, and is provided ywith an internal insulating sleeve 54, as may be seen in FIG. 8. A cylindrical conductor 56 is mounted within the insulating sleeve 54 and projects `axially therefrom into engagement with -a contact strip or brush 58 mounted on an insulating member 60 on the back plate 14. A wire 62 leads to the brush 58 for conducting electrioal oscillations from an amplifier and tone generator thereto. The insulatingsleeve 54 and tubular shaft l28 are provided with a radial opening through which -a wire 64 extends from the conductive cylinder 56 to the loud speakers 42 in parallel. The opposite terminal of each speaker 42 is grounded to the bracket 36. In order to insure a proper return to the frame 12, the grounded output connection of theamplier being connected thereto, a 4-wire or brush 66 (FIG. 8) bears against the side of the extending end .of the shaft 28. The wire or brush 66 is mounted as on a stud 68 threaded or otherwise affixed in the plate 14, and is held against the periphery of the :tubular shaft 28 by a tension spring 70 stretched between the end of the brush 66 and a fixed point 72 on the plate.

The shaft 28 extends through the front plate 14, and a rather large diameter pulley 74 is fixed thereon. A motor 76 is mounted at an upper corner of the `frame 12 by means of la bracket 78, and a rather small pulley 80 is fixed on the motor output shaft. A drive belt 82 passes over the pulleys 74 and 80 to drive lthe frame 30 and speakers 42 at a reduced rate of speed. The repetition rate of the vibrato frequency is determined by the angular velocity of the arm. It has been found that a vibrato frequency of six to eight c.p.s. is desirable, and hence the speed of rotation o-f the frame 4d and speakers 42 preferably is on the order of six to eight c.p.s. The extent of frequency deviation is controlled by the distance the speakers are spaced out from the center of rotation.

Means is provided in the tremulant and vibrato device for producing an amplitude or volume tremulant in the bass tones. Such means comprises an inductance .or solenoid 84 fixed on the front plate 14, and having an axially movable core 86. The inductfance of the solenoid 84 is determined by the position of the core S6, and the core 86 is pivotally connected to -a connecting rod 88 having the opposite end thereof mounted on a crank pin 9i) on the front face of the pulley 74. Accordingly, the inductance of the solenoid 84 is repeatedly changed at the same rate as the vibrato. This inductance is connected in series with a bass speaker by means of wires 89.

Having one form of the mechanical embodiment of the invention in mind, attention should now be directed to FIG. 1. In FIG. 1 there are schematically shown tone gener-ators 92. These tone generators may be of any suitable type generating electric oscillations corresponding to musical tones, for example, tube oscillators. The oscillators may be keyed on or off, or may operate continuously `and connected through key switches, in accordance with any suitable known construction. In any event, the tone generators are connected, as at 94, to an organ amplifier 96 -of any suitable construction. The organ amplifier is connected at 98 to a vibrato control 100. When the vibrato control is in the o1 position, all of the oscillations are connected through a wire 102 to a bass speaker 104 in the organ console. However, when the vibrato control is in the on posit-ion, all of the tones are connected through a wire 106 to a cross-over network 108. There, the tone oscillations are divided into treble and bass. The treble oscillations are connected by the wire 62 to a pair of rotating treble speakers 42 of the type hereinbefore disclosed. The bass tone oscillations are connected -by means of one of the wires 89 to a bass tremolo generator comprising the solenoid 84, the other wire 89 returning the bass ytones to the vibrato control. The bass /tone oscillations are now connected through the vibrato control to the wire 102. Accordingly, the amplitude of the bass tones is varied in accordance with the inductance of the solenoid S4, whereby to produce a tremulant in the bass tones. Simultaneously, the rotating treble speakers 42 produce a vibrato in the treble tones at the same rate as the tremulant.

A more complex embodiment of the invention is illustrated in FIG. 2. In this illustration of the invention, an auxiliary tone cabinet is provided. This tone cabinet is shown at 110 in FIG. 3. The console 110 comprises a generally rectangular cabinet having a substantially square cross-section. The console includes a shallow compartment 112 at the top thereof opening through louvers 114 covered with grill cloth 11-6 on three sides. The rotating treble speakers 42 are mounted in this compartment in horizontal position for rotation about a vertical axis.

A bass speaker 120 opens through a grill-cloth-covered opening in the front of the cabinet or console. The back of the console below the shallow compartment 112 may be open, or the cabinet may be closed at the back and suitably ported, or otherwise constructed for obtaining the desired bass tone reproduction. The cabinet may also contain an auxiliary amplifier 126. Fixed treble speakers 128 also are supported in the console, preferably in the central compartment and opening through the front of the console, preferably being covered with grill cloth.

As may be seen in FIG. 2, the -tone generators 92 remain as in FIG. 1, being connected by a cable or the like 94 to the organ amplifier 96. The circuitchanges somewhat from here, the organ amplifier being connected by means of a wire or the like 130 to an auxiliary amplifier 126. This auxiliary amplifier is connected by means of a wire 132 to a cross-over network 103 of the type in FIG. l. The treble oscillations from the cross-over network are connected by a wire 134 to a vibrato control 136 of somewhat different nature than the one previously mentioned. The bass oscillations are connected by a wire 13S to the vibrato control, and the bass tremolo generator 84 is connected to the vibrato control 136 by wires 14%. The treble oscillations are connected alternatively to stationary treble speakers 142 by means of a wire 144, or to the treble rotating speakers 42 by means of the wire 62. The bass oscillations are connected from the vibrato control to the stationary bass speaker 120 by means of a wire 146.

When the vibrato control is off, the treble tone oscillations are connected by the vibrato control 136 to the stationary treble speakers 142. Similarly, the bass oscillations are simply connected by the vibrato control to the bass speaker 120 without any tremulant being applied thereto. However, when the vibrato control is turned on, the treble oscillations are switched from the stationary speakers 142 to the rotating speakers 42. Simultaneously, the bass tremolo generator 84 (more properly termed a tremulant generator) is connected into circuit to produce tremulant tones in the bass speaker. The rotating treble speakers 42 rotate at all times that the unit is turned on, whereby to avoid the inherent mechanical time lag in starting up the speakers in rotation.

Tests have been made to determine the efficacy of the rotating speakers when rotating about a horizontal axis or about a vertical axis. It has been found that the difference in audible effects is negligible. Accordingly, the auxiliary console is provided with the speakers rotating in a horizontal plane about a vertical axis for reasons of space considerations. Similarly, when the speakers are mounted directly in the organ cabinet or console they are mounted for rotation in a vertical plane about a horizontal axis. This makes for a very compact unit.

Playing of the treble tones and of the bass tones through separate speakers leads to interesting binaural elfects which can be varied by placement of the tone cabinet.

A modification of the setup of the rotating treble speakers is shown in FIG. 7 which may produce interesting vibrato effects. In this embodiment, similar parts are identilied by numerals similar to those heretofore used but with the addition of the suffix a. Thus, the parts all are the same, except that there is a single treble speaker at each end of the rotating frame 30a facing in the direction of rotation. In this instance, the repetition rate is equal to twice the angular velocity in revolutions per second. For a given repetition rate, this automatically reduces the maximum Doppler effect by a factor of two because of the reduction in the instantaneous linear velocity. Obviously, this can be increased without changing the angular velocity by increasingthe arm length. However,vmechanical considerations generally dictate the minimum dimensions available, and for this reason the single set of speakers at only one end of the rotating frame .is to be preferred. Additionally, the back waves from the speakers may tend to produce partial cancellation which would not be produced by the embodiment of FIG. 5.

Since the ultimate Doppler effect observed is Vdependent upon the relative motion between the source and the observer, and since the frequencies and speakers involved are directional, the maximum Doppler effect for a given arm length can be achieved by orienting a speaker so that its beam is coincident with a tangent to the arc described by the arm (i.e. at right angles to the arm). and in the plane of rotation. This is the orientation heretofore shown and described. A minimum Doppler effect occurs if the speaker sound is ydirected radially. This is undesirable, since the best vibrato is produced with maximum Doppler effect. The Doppler effect is further enhanced by mounting of the two speakers 42 back to back at the end of the rotating frame. In this manner, both the increased and decreased frequency eects are transmitted directly to the observer with a minimum of reflection.

Although the principal effect desired is frequency modulation of the signal, there is also a certain amount of arnplitude modulation present because of the directional qualities of the system. A most pleasing musical effect is produced.

The length of the radius about which the treble speaker or speakers rotate is important, and the length is not entirely definite with a four inch speaker mounted as shown. The narrower the speaker (radially of the rotating system) the better, in order for the speaker to approximate a line or point source of sound. The area of a round speaker presents a rather vague dimension of sound source, and causes a certain amount of distortion. Somewhat better results can be obtained by using an oval speaker 42h, as shown in FIG. 9. The speaker is mounted with the narrow dimension oriented radially of the rotating system. This speaker may be two by four, or two by six inches, or perhaps with an even longer maximum dimension. The important thing is that the radial dimension is as small as possible, and that the long dimension is parallel to the axis of rotation.

lt will be observed that in each instance the rotatable speaker or speakers pass forwardly of the axis of rotation, and then rearwardly thereof, relative to an observer or listener. Thus, the speakers alternately approach and recede from the observer, producing a substantial Doppler effect, and the desired vibrato. The axes of the speakers are transverse of the axis of rotation. This is clearly distinguished from a case in which two speakers might be mounted on opposite sides of a rotational axis with the speaker axes parallel to the axis of rotation. Such a system would obviously only move the speakers from side to side relative to an observer, and would be incapable of producing any substantial Doppler effect.

It will also be observed that the use of a small speaker is important. Furthermore, application of the frequency vibrato to only the treble tones is important. The small speaker or speakers are fairly small relative to the diameter of the circle through which they are rotated. Within some limits, the farther the sound source moves the better, and the small speakers allow the sound source to approach either a point or a line source. Using small speakers results in minimum rotating mass, which also makes a reduction in the mass of the counterweight required. In addition, the small speakers are well suited to handling the mid and high frequencies. The use of a small speaker also simplifies calculation of Doppler effect for a given arm length. A large speaker is apt to produce a range of Doppler effects because the difference between the instantaneous velocities relative to the observer of the portions of the speaker nearest and farthest from the center of rotation will be appreciable. This is caused by the fact that the dimensions of a large speaker are appreciable with respect to the length of arm required for a compact cabinet. In addition, to handle the lower frequencies, greater speaker baffling is required which would also increase the weight of the rotating speaker system.

The vibrato from Doppler effects is especially desirable above frequencies of approximately 300 cycles per second because the constant percentage frequency shift allows the simple attainment of greater frequency shifts at the desired repetition rate than can be obtained from amplitude modulation.

Below this figure of approximately 300 cycles per second the Doppler effect still produces a constant percentage frequency shift but a larger fixed frequency shift can be obtained by the use of the amplitude modulation derived from the electro-mechanical variable impedance. In this range, at the desired repetition rate, a more pronounced tremulant can be obtained from amplitude modulation. The percentage modulation can be controlled to control the audible depth of the amplitude modulated tremulant.

In the illustrative examples, the vibrato is produced by frequency modulating the treble tones at a repetition rate of approximately six c.p.s. The frequency deviation is between 2 and 3 percent of the frequency of each note modulated. The bass tremulant, of course, is at the same frequency. The directional qualities of the rotating system also produce a certain amount of amplitude modulation in the treble tones. The audible effect is to produce a true vibrato with a distant singing effect similar to that produced by an expert musician on a musical instrument such as the violin.

The specific examples of the invention as herein shown and described will be understood as being for explanatory purposes only. Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the invention, insofar as they fall within the spirit and scope of the appended claims.

The invention is claimed as follows:

l. An electro-acoustic transducing system for producing vibrato effects comprising base means, rotary support means, means rotatably mounting said rotary support means on said base means for rotation about a predetermined axis, drive means acting between said base means and said rotary support means to rotate said support means, a loud speaker on said support means displaced from the axis of rotation of said support means, the axis of said loud speaker being substantially transverse of the axis of rotation of said support means, a bass loud speaker, an electro-mechanical device electrically connected to said bass loud speaker for producing a tremolo therein, and mechanical means connecting said electro-mechanical device to said drive means to produce a bass tremulant at a frequency related to the rotation of said mounting means.

2. An electro-acoustic transducing system as set forth in claim l wherein the electro-mechanical device comprises a variable impedance element.

3. An electro-acoustic transducing system as set forth in claim 2 wherein the impedance element is a variable inductance.

4. Electro-acoustic tone producing means for producing vibrato effects comprising a tone cabinet having a relatively shallow compartment at the top thereof opening along the edges thereof, rotary treble loud speaker means mounted in said compartment for rotation about a vertical axis with the axis of the loud speaker means transverse of the axis of rotation, a bass loud speaker in said cabinet below said compartment and opening outwardly thereof, fixed treble loud speaker means in said cabinet, tone generator means generating electric oscillations corresponding to musical tones and including bass and treble oscillations, vibrato control means alternatively connecting the treble oscillations to the fixed treble loud speaker means and said rotary loud speaker means, -a variable impedance element, and means interconnecting said rotary loud speaker means and said variable impedance element for varying the impedance of said variable impedance element at a rate related to the speed of rotation of said rotary loud speaker means, said vibrato control means alternatively connecting said variable impedance element between the bass oscillations and the bass loud speaker and for connecting the bass oscillations direct to said bass loud speaker without said variable impedance element.

5. Electro-acoustic tone producing means for producing vibrato effects comprising tone generator means for producing electrical oscillations corresponding to musical tones, including treble tone oscillations and bass tone oscillations, fixed loud speaker means, rotary loud speaker means rotatable about a predetermined axis with the axis of the rotary loud speaker means tranverse of the axis of rotation, drive means for rotating said rotary loud speaker means, amplifier means electrically connected to said generator means, a cross-over network electrically connected to said amplifier means, means electrically connecting the bass tone oscillations from the crossover network to the fixed loud speaker means, means electrically connecting the treble tone oscillations from the cross-over network to the rotary loud speaker means, a variable impedance element connected between the iixed loud speaker means and the cross-over network and in series with the fixed loud speaker means, and means operative from said drive means for Varying said impedance element at a rate related to the speed of rotation of said rotary loud speaker means.

6. Electro-acoustic tone producing means for producing vibrato eflects comprising tone generator means for producing electrical oscillations corresponding to musical tones, including treble tone oscillations and bass tone oscillations, fixed loud speaker means, rotary loud speaker means rotatable about a predetermined axis with the axis of the rotary loud speaker means, amplifier means electrically connected `to said generator means, means electrically connecting the bass tone oscillations from the amplifier' means to the fixed loud speaker means, means electrically connecting the treble tone oscillations from the `amplifier means to the rotary loud speaker means, a variable impedance element connected between the fixed loud speaker means and the amplier means and in series with the fixed loud speaker means, and means operative from said drive means for varying said impedance element 5i at a rate related to the speed of rotation of said rotary loud speaker means.

7. An electro-acoustic transducing system `for producing vibrato etects comprising base means, rotary support means, means rotatably mounting said rotary support means on said base means, drive means acting between said base means and said rotary support means to rotate said support means, and a pair of electrically connected loudspeakers in parallel and in phase on said support means displaced from the axis of rotation of said support means, said pair of loudspeakers being located substantially in a common plane transverse of the axis of rotation of said support means, said loudspeakers lying on opposite sides of a diametral plane through the axis of rotation and facing in opposite directions away from said plane, said loudspeakers having their axes disposed substantially tangentially of the path of rotation.

8. An electro-acoustic transducing system as set forth in claim 7 wherein the loudspeakers are mounted back to back.

9. An electro-acoustic transducing system as set forth in claim 7 wherein the loudspeakers are physically mounted 180 degrees apart.

10. An electro-acoustic transducing system as set forth in claim 7 wherein the loudspeakers are longer in the direction of the axis of rotation than tangentially thereof.

References Cited in the le of this patent UNITED STATES PATENTS 

